We mixed yeast, sugar, and water together in the bottle. To keep the mixture warm we set the bottle in the bowl of warm water.

We drew a small pumpkin on a balloon using a permanent marker and then stretched the balloon over the mouth of the bottle containing the yeast mixture. Then we placed it in the center of the table where it wouldn’t be disturbed and we could all see it.

I set a timer for every 10 minutes so we could check on its progress and watch the balloon get bigger and bigger!

Halloween Science for Kids

The mixture should start to bubble within the first few minutes. These bubbles are the result of the chemical reaction between yeast and sugar.

Yeast is a microbe that “eats” sugar when it is wet and warm. As it “eats” it gives off carbon dioxide, which are the bubble you see. This carbon dioxide gets trapped in the balloon over the top of the bottle, which makes it inflate!

As the minutes tick by you should also start to see the mixture bubble up and grow higher and higher in the bottle. After about an hour it is done reacting (we call this equilibrium) and the mixture recedes back to the bottom of the bottle. However, the balloon stays inflated as long as the seal with the bottle is tight.

This is the exact same reaction that happens whenever someone makes bread, rolls, breadsticks, pizza crust, or cinnamon rolls. As the dough rises (AKA as this yeast reaction occurs) it produces carbon dioxide bubbles, but they get trapped inside the dough. This makes the dough expand, so when you bake it, you have a fluffy, soft texture to bite into. YUM!

More Halloween STEM for Kids

If you are looking for even MORE fun and educational Halloween activities, be sure to check out STEAM Kids Halloween! It contains 50+ pages of spooky fun STEAM (Science, Technology, Engineering, Art & Math) activities that will wow the boredom right out of kids!